The inter-alpha inhibitor protein (IαIp) family is a group of plasma-associated serine protease inhibitors. Members of this family are composed of heavy and light polypeptide subunits that are covalently linked by a glycosaminoglycan. The light chain, also called bikunin, is responsible for the serine protease inhibitory activity of the molecules. The name “bikunin” reflects the presence of 2 protease-inhibiting domains of the Kunitz type. In normal plasma, bikunin is found mostly in a complex form as inter-alpha inhibitor (IαI), which has a molecular weight of 225 kDa, and pre-alpha inhibitor (PαI), which has molecular weight of 120 kDa. In IαI, bikunin is linked to 2 heavy polypeptide chains, H1 and H2, whereas, in PαI, only a single heavy chain (H3) is linked to bikunin. In these complexed forms, bikunin remains inactive until its release by partial proteolytic degradation, a mechanism that serves as a means to regulate activity. After cleavage from the complex, the activated bikunin is cleared rapidly from plasma by glomerular filtration, a process that is facilitated by its low molecular weight and by receptor-mediated uptake. U.S. Pat. Nos. 6,489,128 and 6,660,482 are related to the use of diagnosing cancer and sepsis, respectively. Methods of inhibiting metastases and of treating sepsis are also disclosed, however, the compositions were not substantially pure and had stability, i.e., short half-lives, problems.
Despite the introduction of antibiotics over fifty years ago, which indeed saw a decline of sepsis-induced mortality from 55% to 35%, medicine has not benefited from a significant reduction in mortality of subjects with sepsis. In fact, sepsis continues to be one of the leading causes of death in intensive care units and a large number of septic subjects die of ensuing septic shock and multiple organ failure. Sepsis is a systemic response to infection, e.g., a bacterial infection. It is commonly caused by endotoxins from Gram negative bacteria or exotoxins from Gram positive bacteria (which can trigger endotoxin-like responses). The systemic response can lead to septic shock, which is characterized by a precipitous drop in blood pressure, cardiovascular collapse, and/or multiple organ failure. The mortality rate among subjects diagnosed with septic shock can be as high as 35-45%. Rapidly and reliably treating sepsis has been difficult using conventional medications.
Sepsis and septic shock are associated with activation of innate immunity and coagulation systems. Sepsis and septic shock are characterized clinically by systemic inflammation, coagulopathy, hypotension and multiple organ dysfunction (J.-L. Vincent et al., Annuals of Medicine 34 (2002) 606-613). During severe sepsis, a network of specific proteases activates clotting, fibrinolytic and complement factors. These proteases can also trigger tissue and organ damage and enhance non-specific proteolysis of clotting and complement factors in plasma (J. Wite et al., Intensive Care Medicine 8 (1982) 215-222; S. J. Weiss, New England Journal of Medicine 320 (1989) 365-376).